#include <seminix/bitmap.h>
#include <seminix/bug.h>
#include <seminix/idr.h>
#include <seminix/slab.h>
#include <seminix/spinlock.h>
#include <seminix/xarray.h>

/**
 * idr_alloc_u32() - Allocate an ID.
 * @idr: IDR handle.
 * @ptr: Pointer to be associated with the new ID.
 * @nextid: Pointer to an ID.
 * @max: The maximum ID to allocate (inclusive).
 * @gfp: Memory allocation flags.
 *
 * Allocates an unused ID in the range specified by @nextid and @max.
 * Note that @max is inclusive whereas the @end parameter to idr_alloc()
 * is exclusive.  The new ID is assigned to @nextid before the pointer
 * is inserted into the IDR, so if @nextid points into the object pointed
 * to by @ptr, a concurrent lookup will not find an uninitialised ID.
 *
 * The caller should provide their own locking to ensure that two
 * concurrent modifications to the IDR are not possible.  Read-only
 * accesses to the IDR may be done under the RCU read lock or may
 * exclude simultaneous writers.
 *
 * Return: 0 if an ID was allocated, -ENOMEM if memory allocation failed,
 * or -ENOSPC if no free IDs could be found.  If an error occurred,
 * @nextid is unchanged.
 */
int idr_alloc_u32(struct idr *idr, void *ptr, u32 *nextid,
            unsigned long max, gfp_t gfp)
{
    struct radix_tree_iter iter;
    void __rcu **slot;
    unsigned int base = idr->idr_base;
    unsigned int id = *nextid;

    if (WARN_ON_ONCE(!(idr->idr_rt.xa_flags & ROOT_IS_IDR)))
        idr->idr_rt.xa_flags |= IDR_RT_MARKER;

    id = (id < base) ? 0 : id - base;
    radix_tree_iter_init(&iter, id);
    slot = idr_get_free(&idr->idr_rt, &iter, gfp, max - base);
    if (IS_ERR(slot))
        return PTR_ERR(slot);

    *nextid = iter.index + base;
    /* there is a memory barrier inside radix_tree_iter_replace() */
    radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
    radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);

    return 0;
}

/**
 * idr_alloc() - Allocate an ID.
 * @idr: IDR handle.
 * @ptr: Pointer to be associated with the new ID.
 * @start: The minimum ID (inclusive).
 * @end: The maximum ID (exclusive).
 * @gfp: Memory allocation flags.
 *
 * Allocates an unused ID in the range specified by @start and @end.  If
 * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
 * callers to use @start + N as @end as long as N is within integer range.
 *
 * The caller should provide their own locking to ensure that two
 * concurrent modifications to the IDR are not possible.  Read-only
 * accesses to the IDR may be done under the RCU read lock or may
 * exclude simultaneous writers.
 *
 * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
 * or -ENOSPC if no free IDs could be found.
 */
int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
    u32 id = start;
    int ret;

    if (WARN_ON_ONCE(start < 0))
        return -EINVAL;

    ret = idr_alloc_u32(idr, ptr, &id, end > 0 ? end - 1 : INT_MAX, gfp);
    if (ret)
        return ret;

    return id;
}

/**
 * idr_alloc_cyclic() - Allocate an ID cyclically.
 * @idr: IDR handle.
 * @ptr: Pointer to be associated with the new ID.
 * @start: The minimum ID (inclusive).
 * @end: The maximum ID (exclusive).
 * @gfp: Memory allocation flags.
 *
 * Allocates an unused ID in the range specified by @nextid and @end.  If
 * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
 * callers to use @start + N as @end as long as N is within integer range.
 * The search for an unused ID will start at the last ID allocated and will
 * wrap around to @start if no free IDs are found before reaching @end.
 *
 * The caller should provide their own locking to ensure that two
 * concurrent modifications to the IDR are not possible.  Read-only
 * accesses to the IDR may be done under the RCU read lock or may
 * exclude simultaneous writers.
 *
 * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
 * or -ENOSPC if no free IDs could be found.
 */
int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
    u32 id = idr->idr_next;
    int err, max = end > 0 ? end - 1 : INT_MAX;

    if ((int)id < start)
        id = start;

    err = idr_alloc_u32(idr, ptr, &id, max, gfp);
    if ((err == -ENOSPC) && (id > start)) {
        id = start;
        err = idr_alloc_u32(idr, ptr, &id, max, gfp);
    }
    if (err)
        return err;

    idr->idr_next = id + 1;
    return id;
}

/**
 * idr_remove() - Remove an ID from the IDR.
 * @idr: IDR handle.
 * @id: Pointer ID.
 *
 * Removes this ID from the IDR.  If the ID was not previously in the IDR,
 * this function returns %NULL.
 *
 * Since this function modifies the IDR, the caller should provide their
 * own locking to ensure that concurrent modification of the same IDR is
 * not possible.
 *
 * Return: The pointer formerly associated with this ID.
 */
void *idr_remove(struct idr *idr, unsigned long id)
{
    return radix_tree_delete_item(&idr->idr_rt, id - idr->idr_base, NULL);
}

/**
 * idr_find() - Return pointer for given ID.
 * @idr: IDR handle.
 * @id: Pointer ID.
 *
 * Looks up the pointer associated with this ID.  A %NULL pointer may
 * indicate that @id is not allocated or that the %NULL pointer was
 * associated with this ID.
 *
 * This function can be called under rcu_read_lock(), given that the leaf
 * pointers lifetimes are correctly managed.
 *
 * Return: The pointer associated with this ID.
 */
void *idr_find(const struct idr *idr, unsigned long id)
{
    return radix_tree_lookup(&idr->idr_rt, id - idr->idr_base);
}

/**
 * idr_for_each() - Iterate through all stored pointers.
 * @idr: IDR handle.
 * @fn: Function to be called for each pointer.
 * @data: Data passed to callback function.
 *
 * The callback function will be called for each entry in @idr, passing
 * the ID, the entry and @data.
 *
 * If @fn returns anything other than %0, the iteration stops and that
 * value is returned from this function.
 *
 * idr_for_each() can be called concurrently with idr_alloc() and
 * idr_remove() if protected by RCU.  Newly added entries may not be
 * seen and deleted entries may be seen, but adding and removing entries
 * will not cause other entries to be skipped, nor spurious ones to be seen.
 */
int idr_for_each(const struct idr *idr,
        int (*fn)(int id, void *p, void *data), void *data)
{
    struct radix_tree_iter iter;
    void __rcu **slot;
    int base = idr->idr_base;

    radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
        int ret;
        unsigned long id = iter.index + base;

        if (WARN_ON_ONCE(id > INT_MAX))
            break;
        ret = fn(id, rcu_dereference_raw(*slot), data);
        if (ret)
            return ret;
    }

    return 0;
}

/**
 * idr_get_next() - Find next populated entry.
 * @idr: IDR handle.
 * @nextid: Pointer to an ID.
 *
 * Returns the next populated entry in the tree with an ID greater than
 * or equal to the value pointed to by @nextid.  On exit, @nextid is updated
 * to the ID of the found value.  To use in a loop, the value pointed to by
 * nextid must be incremented by the user.
 */
void *idr_get_next(struct idr *idr, int *nextid)
{
    struct radix_tree_iter iter;
    void __rcu **slot;
    unsigned long base = idr->idr_base;
    unsigned long id = *nextid;

    id = (id < base) ? 0 : id - base;
    slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);
    if (!slot)
        return NULL;
    id = iter.index + base;

    if (WARN_ON_ONCE(id > INT_MAX))
        return NULL;

    *nextid = id;
    return rcu_dereference_raw(*slot);
}

/**
 * idr_get_next_ul() - Find next populated entry.
 * @idr: IDR handle.
 * @nextid: Pointer to an ID.
 *
 * Returns the next populated entry in the tree with an ID greater than
 * or equal to the value pointed to by @nextid.  On exit, @nextid is updated
 * to the ID of the found value.  To use in a loop, the value pointed to by
 * nextid must be incremented by the user.
 */
void *idr_get_next_ul(struct idr *idr, unsigned long *nextid)
{
    struct radix_tree_iter iter;
    void __rcu **slot;
    unsigned long base = idr->idr_base;
    unsigned long id = *nextid;

    id = (id < base) ? 0 : id - base;
    slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);
    if (!slot)
        return NULL;

    *nextid = iter.index + base;
    return rcu_dereference_raw(*slot);
}

/**
 * idr_replace() - replace pointer for given ID.
 * @idr: IDR handle.
 * @ptr: New pointer to associate with the ID.
 * @id: ID to change.
 *
 * Replace the pointer registered with an ID and return the old value.
 * This function can be called under the RCU read lock concurrently with
 * idr_alloc() and idr_remove() (as long as the ID being removed is not
 * the one being replaced!).
 *
 * Returns: the old value on success.  %-ENOENT indicates that @id was not
 * found.  %-EINVAL indicates that @ptr was not valid.
 */
void *idr_replace(struct idr *idr, void *ptr, unsigned long id)
{
    struct radix_tree_node *node;
    void __rcu **slot = NULL;
    void *entry;

    id -= idr->idr_base;

    entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
    if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
        return ERR_PTR(-ENOENT);

    __radix_tree_replace(&idr->idr_rt, node, slot, ptr);

    return entry;
}

/**
 * DOC: IDA description
 *
 * The IDA is an ID allocator which does not provide the ability to
 * associate an ID with a pointer.  As such, it only needs to store one
 * bit per ID, and so is more space efficient than an IDR.  To use an IDA,
 * define it using DEFINE_IDA() (or embed a &struct ida in a data structure,
 * then initialise it using ida_init()).  To allocate a new ID, call
 * ida_alloc(), ida_alloc_min(), ida_alloc_max() or ida_alloc_range().
 * To free an ID, call ida_free().
 *
 * ida_destroy() can be used to dispose of an IDA without needing to
 * free the individual IDs in it.  You can use ida_is_empty() to find
 * out whether the IDA has any IDs currently allocated.
 *
 * The IDA handles its own locking.  It is safe to call any of the IDA
 * functions without synchronisation in your code.
 *
 * IDs are currently limited to the range [0-INT_MAX].  If this is an awkward
 * limitation, it should be quite straightforward to raise the maximum.
 */

/*
 * Developer's notes:
 *
 * The IDA uses the functionality provided by the XArray to store bitmaps in
 * each entry.  The XA_FREE_MARK is only cleared when all bits in the bitmap
 * have been set.
 *
 * I considered telling the XArray that each slot is an order-10 node
 * and indexing by bit number, but the XArray can't allow a single multi-index
 * entry in the head, which would significantly increase memory consumption
 * for the IDA.  So instead we divide the index by the number of bits in the
 * leaf bitmap before doing a radix tree lookup.
 *
 * As an optimisation, if there are only a few low bits set in any given
 * leaf, instead of allocating a 128-byte bitmap, we store the bits
 * as a value entry.  Value entries never have the XA_FREE_MARK cleared
 * because we can always convert them into a bitmap entry.
 *
 * It would be possible to optimise further; once we've run out of a
 * single 128-byte bitmap, we currently switch to a 576-byte node, put
 * the 128-byte bitmap in the first entry and then start allocating extra
 * 128-byte entries.  We could instead use the 512 bytes of the node's
 * data as a bitmap before moving to that scheme.  I do not believe this
 * is a worthwhile optimisation; Rasmus Villemoes surveyed the current
 * users of the IDA and almost none of them use more than 1024 entries.
 * Those that do use more than the 8192 IDs that the 512 bytes would
 * provide.
 *
 * The IDA always uses a lock to alloc/free.  If we add a 'test_bit'
 * equivalent, it will still need locking.  Going to RCU lookup would require
 * using RCU to free bitmaps, and that's not trivial without embedding an
 * RCU head in the bitmap, which adds a 2-pointer overhead to each 128-byte
 * bitmap, which is excessive.
 */

/**
 * ida_alloc_range() - Allocate an unused ID.
 * @ida: IDA handle.
 * @min: Lowest ID to allocate.
 * @max: Highest ID to allocate.
 * @gfp: Memory allocation flags.
 *
 * Allocate an ID between @min and @max, inclusive.  The allocated ID will
 * not exceed %INT_MAX, even if @max is larger.
 *
 * Context: Any context.
 * Return: The allocated ID, or %-ENOMEM if memory could not be allocated,
 * or %-ENOSPC if there are no free IDs.
 */
int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max,
            gfp_t gfp)
{
    XA_STATE(xas, &ida->xa, min / IDA_BITMAP_BITS);
    unsigned bit = min % IDA_BITMAP_BITS;
    unsigned long flags;
    struct ida_bitmap *bitmap, *alloc = NULL;

    if ((int)min < 0)
        return -ENOSPC;

    if ((int)max < 0)
        max = INT_MAX;

retry:
    xas_lock_irqsave(&xas, flags);
next:
    bitmap = xas_find_marked(&xas, max / IDA_BITMAP_BITS, XA_FREE_MARK);
    if (xas.xa_index > min / IDA_BITMAP_BITS)
        bit = 0;
    if (xas.xa_index * IDA_BITMAP_BITS + bit > max)
        goto nospc;

    if (xa_is_value(bitmap)) {
        unsigned long tmp = xa_to_value(bitmap);

        if (bit < BITS_PER_XA_VALUE) {
            bit = find_next_zero_bit(&tmp, BITS_PER_XA_VALUE, bit);
            if (xas.xa_index * IDA_BITMAP_BITS + bit > max)
                goto nospc;
            if (bit < BITS_PER_XA_VALUE) {
                tmp |= 1UL << bit;
                xas_store(&xas, xa_mk_value(tmp));
                goto out;
            }
        }
        bitmap = alloc;
        if (!bitmap)
            bitmap = kzalloc(sizeof(*bitmap), GFP_KERNEL);
        if (!bitmap)
            goto alloc;
        bitmap->bitmap[0] = tmp;
        xas_store(&xas, bitmap);
        if (xas_error(&xas)) {
            bitmap->bitmap[0] = 0;
            goto out;
        }
    }

    if (bitmap) {
        bit = find_next_zero_bit(bitmap->bitmap, IDA_BITMAP_BITS, bit);
        if (xas.xa_index * IDA_BITMAP_BITS + bit > max)
            goto nospc;
        if (bit == IDA_BITMAP_BITS)
            goto next;

        __set_bit(bit, bitmap->bitmap);
        if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS))
            xas_clear_mark(&xas, XA_FREE_MARK);
    } else {
        if (bit < BITS_PER_XA_VALUE) {
            bitmap = xa_mk_value(1UL << bit);
        } else {
            bitmap = alloc;
            if (!bitmap)
                bitmap = kzalloc(sizeof(*bitmap), GFP_KERNEL);
            if (!bitmap)
                goto alloc;
            __set_bit(bit, bitmap->bitmap);
        }
        xas_store(&xas, bitmap);
    }
out:
    xas_unlock_irqrestore(&xas, flags);
    if (xas_nomem(&xas, gfp)) {
        xas.xa_index = min / IDA_BITMAP_BITS;
        bit = min % IDA_BITMAP_BITS;
        goto retry;
    }
    if (bitmap != alloc)
        kfree(alloc);
    if (xas_error(&xas))
        return xas_error(&xas);
    return xas.xa_index * IDA_BITMAP_BITS + bit;
alloc:
    xas_unlock_irqrestore(&xas, flags);
    alloc = kzalloc(sizeof(*bitmap), gfp);
    if (!alloc)
        return -ENOMEM;
    xas_set(&xas, min / IDA_BITMAP_BITS);
    bit = min % IDA_BITMAP_BITS;
    goto retry;
nospc:
    xas_unlock_irqrestore(&xas, flags);
    return -ENOSPC;
}

/**
 * ida_free() - Release an allocated ID.
 * @ida: IDA handle.
 * @id: Previously allocated ID.
 *
 * Context: Any context.
 */
void ida_free(struct ida *ida, unsigned int id)
{
    XA_STATE(xas, &ida->xa, id / IDA_BITMAP_BITS);
    unsigned bit = id % IDA_BITMAP_BITS;
    struct ida_bitmap *bitmap;
    unsigned long flags;

    BUG_ON((int)id < 0);

    xas_lock_irqsave(&xas, flags);
    bitmap = xas_load(&xas);

    if (xa_is_value(bitmap)) {
        unsigned long v = xa_to_value(bitmap);
        if (bit >= BITS_PER_XA_VALUE)
            goto err;
        if (!(v & (1UL << bit)))
            goto err;
        v &= ~(1UL << bit);
        if (!v)
            goto delete;
        xas_store(&xas, xa_mk_value(v));
    } else {
        if (!test_bit(bit, bitmap->bitmap))
            goto err;
        __clear_bit(bit, bitmap->bitmap);
        xas_set_mark(&xas, XA_FREE_MARK);
        if (bitmap_empty(bitmap->bitmap, IDA_BITMAP_BITS)) {
            kfree(bitmap);
delete:
            xas_store(&xas, NULL);
        }
    }
    xas_unlock_irqrestore(&xas, flags);
    return;
 err:
    xas_unlock_irqrestore(&xas, flags);
    WARN(1, "ida_free called for id=%d which is not allocated.\n", id);
}

/**
 * ida_destroy() - Free all IDs.
 * @ida: IDA handle.
 *
 * Calling this function frees all IDs and releases all resources used
 * by an IDA.  When this call returns, the IDA is empty and can be reused
 * or freed.  If the IDA is already empty, there is no need to call this
 * function.
 *
 * Context: Any context.
 */
void ida_destroy(struct ida *ida)
{
    XA_STATE(xas, &ida->xa, 0);
    struct ida_bitmap *bitmap;
    unsigned long flags;

    xas_lock_irqsave(&xas, flags);
    xas_for_each(&xas, bitmap, ULONG_MAX) {
        if (!xa_is_value(bitmap))
            kfree(bitmap);
        xas_store(&xas, NULL);
    }
    xas_unlock_irqrestore(&xas, flags);
}
